1. Field of the Invention
The present invention relates to a headbox apparatus for a papermaking machine.
More specifically, the present invention relates to a headbox apparatus for a papermaking machine which defines a flow path for stock flowing between an upstream header and a downstream slice lip.
2. Background Information
A conventional headbox distributor uses a tube array to spread the pulp slurry as uniformly as possible across the width of a paper machine headbox prior to the start of the drainage or other thickening process. The tube array is made up of individual round inlet tubes mounted is some manner to cause acceleration of the flow into each tube from a cross machine header or other form of supply of the slurry prior to the tube array. The pressure drop from the acceleration of the flow at the inlet of each tube within the array is critical to the uniformity of the flow within each tube, and therefore to the uniformity of the cross machine uniformity of the headbox in general. This acceleration of the flow is also a factor in the operational cleanliness of the headbox operation. The exit end of a typical tube array may take on many shapes such as round, hexagonal, rectangular, square, or other shape but eventually the flows exiting each individual tube must be re-joined prior to or within the nozzle of the headbox prior to discharge to the drainage area. The reorientation of the round tube entrance flow to the eventual rectangular shape of the nozzle will create disturbances in the flow in all directions. These disturbances must be damped or reduced in some way prior to discharge out of the slice so as to avoid nonuniformities in the paper web.
The purpose of the present invention is to create the necessary pressure drop and subsequent uniform cross machine flow distribution while minimizing the wall effects of the individual flow elements prior to the rejoining of the flows in the nozzle. Additionally, an added feature of accelerating the flow into the headbox nozzle is incorporated into the flow element design to further stabilize the flow exiting the headbox.
The entrance of each flow element is a slot shape and the discharge end of each tube is an open channel of square, rectangular, round or some other geometric shape. These flow elements can also have one or multiple changes in area between the initial flow element slot size and the discharge area of the flow element. Additionally, an added feature of accelerating the flow into the headbox nozzle is incorporated into the flow element design to further stabilize the flow exiting the headbox. The flow elements may or may not be used in conjunction with trailing members. Furthermore, the flow elements may or may not be designed to incorporate or work in conjunction with the use of a consistency profiling system.
The flow elements according to the present invention are nested together to form a close packed array on the discharge end, with little or no vertical wall continuous in any area across the width of the headbox.
To make the edge effect minimal to the pondsides, a special flow element can be supplied on each end which reduces flow instability due to side wall friction. This flow element may be larger in the entrance area than the rest of the flow elements.
Such larger inlet may additionally have an adjustable insert for flow and fiber orientation control.
The present invention uses a distributor consisting of simple slotted flow elements, expanding to another slotted expansion area (one or multiple), then to a larger discharge area. The arrangement according to the present invention will reduce cross machine non uniformity of both consistency and velocity of the stock flow. Additionally, an added feature of accelerating the flow into the headbox nozzle is incorporated into the flow element design to further stabilize the flow exiting the headbox.
The apparatus according to the present invention uses slots to minimize the vertical non uniformity of the open area at the discharge of the flow element and increases mixing of the flows in the cross machine direction at the discharge of the flow elements.
The present invention is applicable to the production of all grades of paper, and is usable with or without the inclusion of flow turbulence control sheets.
The elements according to the present invention can be fabricated out of many different types of materials including synthetic, ceramic, stainless steel, cast material, etc.
Such elements can also be used with or without a dilution control system or with or without the use of trailing members.
Therefore, it is a primary feature of the present invention to provide a headbox apparatus that overcomes the problems associated with the prior art arrangements.
Another feature of the present invention is the provision of a headbox apparatus that greatly reduces the impact of said upstream and downstream vortices on a flow consistency and a velocity uniformity of the stock.
Other features and advantages of the present invention will be readily apparent to those skilled in the art by a consideration of the detailed description of a preferred embodiment of the present invention contained herein.